Justification:
Impoundment of main rivers (all happened more than 10 years ago) has significantly reduced available spawning sites and migration routes. The current threat to the species is overfishing, at sea and in the rivers during the migration runs, which is causing a population decline of unknown levels. The area of the remaining spawning grounds is estimated to be less than 2,000 km² and based on the fishing in the lower courses of rivers during the migration runs, the species is found in six locations (Dneister, Dneiper, Danube, Kuban, Pivdenny Bug and Don).

Black and Azov Seas from where adults ascend rivers, migrating far upstream to spawn. Historically ascended Danube for about 1,600 km to Mohacs (Hungary), Don for 900 km to Oust-Medveditskaya, Dniepr up to Kiev, Dniestr up to Yampol and South Bug up to Voznessensks. A landlocked population in Don.Currently migrates up the Danube, Dneiper, Dneister, Pivdenny Bug, Don and Kuban (not previously used by the species until 1993) where they still spawn below dams.

Habitat: At sea, pelagic, in deep water. Migrates to middle reaches of large rivers, spawning where current is strongest, close to surface, usually at 2-3 m depth in main channel.

Biology: Anadromous, migrating upriver to spawn at three years, rarely earlier. Only few individuals spawn two seasons. Appears along coast in March-April, enters rivers when temperatures reach about 6-9°C, between late March and late April. Migration usually peaks in May. Spawning starts when temperature rises above 15°C, in April-August. Spawns usually between 1 and 8 p.m. Eggs are pelagic. Spent individuals migrate back to sea to feed. Juveniles inhabit floodplain and shallow riverine habitats, migrate to the sea or estuarine habitats during first summer; in autumn, they move to the sea, remaining there until they mature. At sea, feeds on a wide variety of zooplankton (especially crustaceans) and small fish.

Overfishing is the major current threat to the species. It is caught both at sea and in the lower courses of rivers during the migration. Dam construction in the Black Sea basin (over 10 years ago) has led to the loss of large areas of spawning grounds.